I'm not crossing my fingers. Joss is pretty big on finding new actors. Of the main Dollhouse cast (so not counting Amy, who was recurring), only one was an alum; Firefly had none; Angel doesn't really count since all the alums were Buffy characters (and that's the whole point of a spinoff anyway); and Avengers had none (again, in main roles).

I'm guessing the entire supporting cast will be from Sunnydale though.

I'm not crossing my fingers. Joss is pretty big on finding new actors.

I'd describe it more as him having a knack for casting actors who fit his characters really well - which basically amounts to the same thing since the characters in his shows tend to be so well developed. I would add, though, that due to the ever growing nature of the alumnus itself, chance repeat casting is now more likely than ever.

Hypothetically if when Joss was writing the pilot, had there been a character he thought perfect for a previous Whedon actor, we might not know of the character yet as there would be no need for a casting call.

Sean Maher auditioned to play Victor in Dollhouse, and there doesn't seem to be any awkwardness there. I wouldn't be surprised if there are other stories like that we just haven't heard. I like that the cast list is all new names so far.

In the Cabin in the Woods visual companion Fran Kranz talks a bit about auditioning for Marty while still doing Dollhouse. Not knowing whether he got the part was a little akward to him sometimes.

Yes, Nathan Filloin auditioned for Angel but he didn't make it far enough to meet Joss. http://www.youtube.com/watch?v=t5NIRRNYphY I can't find the comments now but he has said that he thought DB did a great job with the role and if he had been cast as Angel he probably wouldn't have gotten to play Mal so it all worked out.

NPH auditioned to play Sean's character on Firefly. He didn't get it, obv.

You have to be really careful when casting as ultimately you need to cast the right person over anything else. The right look, the right skill set, mind set etc. I remember somebody saying James Marsters should play Topher after they read the character breakdown. I don't think that would have worked at all.

That isn't to say the remaining role couldn't be played by somebody from the Whedonverse, btdubs. Because there's certainly some talent there which would fit, in my tiny brain at least.